APL3203D datasheet(14/19 Pages) ANPEC

14 / 19 page

Rev. A.6 - Mar., 2013

www.anpec.com.tw

APL3203D

Application Information

BAT Selection

Connect the BAT pin to the positive terminal of battery

through a resistor R

BAT for battery OVP function. The RBAT

limits the current flowing from BAT to battery in case of

BAT pin is shortened to VIN pin under a failure mode. The

recommended value of R

BAT is 100kΩ. In the worse case

of an IC failure, the current flowing from the BAT pin to the

battery is:

(30V-3V)/ 100k

Ω =270µA

where the 30V is the maximum IN voltage and the 3V is

the minimum battery voltage. The current is so small and

can be absorbed by the charger system.

The disadvantage with the large R

BAT is that the error of

the battery OVP threshold will be increased. The addi-

tional error is the voltage drop across the R

BAT because

of the BAT bias current. When R

BAT is 100kΩ, the worse-

case additional error is 100k

Ωx20nA=2mV, which is ac-

ceptable in most applications.

EN Selection

Since the IO voltage is divided by R

EN and EN internal pull

low resistor for EN voltage. It has to be ensured that the

EN voltage is above the EN logic high voltage when the

GPIO output of the MCU is high.

FAULTOutput

Since the FAULT pin is an open-drain output, connecting

a resistor R

UP to a pull high voltage is necessary. It is also

recommended that connect the FAULT to the MCU GPIO

through a resistor R

FAULT. The RFAULT prevents damage to

the MCU under a failure mode. The recommended value

of the resistors should be between 10k

Ω to 100kΩ.

Capacitor Selection

The input capacitor is for decoupling and prevents the

input voltage from overshooting to dangerous levels. In

the AC adapter hot plug-in applications or load current

step-down transient, the input voltage has a transient

spike due to the parasitic inductance of the input cable. A

25V, X5R, dielectric ceramic capacitor with a value be-

tween 1

µF and 4.7µF placed close to the IN pin is

recommended.

The output capacitor is for output voltage decoupling, and

also can be as the input capacitor of the charging circuit.

At least, a 1

µF, 10V, X5R capacitor is recommended.

For the same reason as the BAT pin case, the EN pin

should be connected to the MCU GPIO pin through a

resistor. The value of the R

EN is dependent on the IO

voltage of the MCU.

In some failure modes, a high voltage may be applied to

the device. Make sure the clearance constraint of the PCB

layout must satisfy the design rule for high voltage.

The exposed pad of the TDFN2x2-8 performs the func-

tion of channeling heat away. It is recommended that

connect the exposed pad to a large copper ground plane

on the backside of the circuit board through several ther-

mal vias to improve heat dissipation.

The input and output capacitors should be placed close

to the IC. R

ILIM also should be placed close to the IC.

The high current traces like input trace and output trace

must be wide and short.

Layout Consideration

BAT

Li+

Battery

FAULT

MCU

FAULT

BAT

VIO

GPIO

Figure 5. R

UP, RFAULT, REN and RBAT

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